1. Field of the Invention
The present invention relates to an airbag gas generator for protecting an occupant from an impact and more specifically to a gas generator which can be reduced in size and weight and can make an efficient use of a filter.
2. Description of the Related Art
An example of a conventional airbag gas generator is illustrated in FIG. 4. The gas generator includes: a housing 31 having gas discharge ports 30; an ignition means accommodating chamber 32 formed in a central part of the housing 31; a combustion chamber 33 formed on the outer side of the ignition means accommodating chamber 32; a coolant filter chamber 34 formed on the outer side of the combustion chamber 33; ignition means, i.e., an igniter 35 and a transfer charge 36, disposed in the ignition means accommodating chamber 32; gas generating means i.e. a canister 38 filled with a gas generating agent 37, disposed in the combustion chamber 33 and to be ignited by the ignition means to generate a gas; a coolant 39 for cooling a combustion gas generated in the combustion chamber 33 and cleaning means for cleaning or purifying the combustion gas, i.e., a filter 40, both disposed in the coolant filter chamber 34.
A plurality of gas discharge ports 30 are formed in the housing 31 in a circumferential direction at predetermined intervals.
The coolant filter chamber 34 is divided by a retainer 42 into an upper tier chamber and a lower tier chamber, the upper tier chamber accommodating the filter 40 and the lower tier chamber accommodating the coolant 39.
When a sensor (not shown) senses an impact, its signal is sent to the igniter 35, which is then activated to ignite the transfer charge 36. The transfer charge 36 when ignited generates high-temperature and high-pressure flames, which pass through openings 41, fractures the wall of the canister 38 and then ignites the gas generating agent 37 contained therein. Then, the gas generating agent 37 burns to generate a gas, which then passes through gas passing ports 44 of a combustor cup 43 and passes through the coolant 39, during which period the gas is cooled and removed of combustion residues. Further as the gas passes through the filter 40, the remaining combustion residues are removed. The cooled and cleaned gas flows through the gas discharge ports 30 into an airbag (not shown). The inflow-gas inflates the airbag, forming a cushion between an occupant and a hard structure to protect the occupant against an impact.
In the conventional gas generator described above, the gas discharge ports are disposed downstream of the filter with respect to the gas flow direction and are formed intermittently at predetermined intervals. Hence, the gas flow that enter and pass through the filter and move out of the housing tend to concentrate toward the gas discharge ports and therefore do not reach the portions of the filter between the adjacent gas discharge ports. As a result, these filter portions are not used effectively. In other words, an efficient utilization cannot be made of the entire area of the filter.
In the above conventional gas generator, the coolant filter chamber where the filter is installed is formed outside the combustion chamber. This construction increases the diameter of the gas generator, which causes a problem of increased size and weight of the gas generator.
An object of this invention is to provide a novel gas generator that solves problems experienced in the prior art described above.
This invention provides an airbag gas generator which comprises: a first member with one end thereof open; a second member closing the open end of the first member; an ignition units and a gas generating agent, both disposed in a container formed by the first and second members; a filter arranged around an outer circumference of the container to enclose gas passing ports formed in the container; and (1) a strip plate member having a width smaller than the width of the filter and adapted to prevent a radial expansion of the filter, or (2) a mesh member covering the filter, both arranged around an outer circumference of the filter.
In the gas generator including the container, the gas passing ports and the filter, (1) the strip plate member or (2) the mesh member is also provided.
The filter is held between the first member and the second member. The filter is arranged along the outer circumference of the container to enclose the gas passing ports formed in the container. The first member and the second member together form the gas discharge port outside the filter. An outer side surface 20 of the filter faces the gas discharge port.
The gas passing through the gas passing ports enters the filter and is then introduced from the gas discharge port into the airbag.
The strip plate member is preferably installed at the gas discharge port, which is therefore defined by the first member, the second member, and the strip plate member. The gas passing ports are preferably disposed not to oppose the gas discharge port in radial direction so that the gas does not flow out straight in radial direction but flows out in a curved path. In other words, the flow path in the filter is preferably extended.
It is preferred that the strip plate member and the mesh member be preferably made of a stainless steel material and that the mesh member has a stainless steel wire mesh covering the entire surface thereof.
(1) The strip plate member is arranged along the outer circumference of the filter and has a width smaller than that of the filter. Hence, there is an uncovered portion of the filter which is not covered by the strip plate member. This uncovered portion functions as a continuous window to allow the gas to pass through the filter when it has entered the filter. This continuous window eliminates a problem that the gas flows tend to concentrate toward gas discharge ports used in the conventional gas generator.
When the gas applies a force to the filter, the filter tends to expand outwardly in radial direction. This tendency is restricted by the strip plate member.
(2) The mesh member is arranged along the outer circumference of the filter to cover the filter. The mesh member allows passage of gas through its entire area. This eliminates the problem of the conventional gas generator in which the gas flow tends to concentrate toward gas discharge ports. The gas flow passing through the filter do not concentrate but passes through the entire area of the mesh member located adjacent to the filter before flowing out into the airbag.
The mesh member may be formed of, for example, laminated layers of stainless steel wire mesh.
With the gas generator of this invention constructed as described above, the gas can pass through the entire area of the filter, thus realizing an efficient use of the filter.
The gas generator of this invention obviates the need for the coolant filter chamber provided in the conventional gas generator. This not only simplifies the construction of the gas generator but reduces the diameter of the gas generator. As a result, the gas generator can be reduced in size and weight.